1. Field of the Invention
The present invention relates to a chip-type resistor element such as a thermistor, and more particularly, to a laminated chip-type resistor element having a plurality of pairs of first and second inner electrodes, the tips of each of the pairs being mutually opposed with a gap interposed therebetween.
2. Description of the Related Art
Conventional chip-type thermistors have been used for temperature compensation or temperature detection. In conventional chip-type thermistor elements, various laminated chip-type thermistor elements have been proposed in order to prevent the fluctuation of electrical characteristics caused by changes in external environment (for example, see Japanese Unexamined Patent Application Publication No. 8-250307).
Also, in Japanese Patent Application No. 9-49256 (i.e., Japanese Unexamined Patent Application Publication No. 10-247601), a chip-type thermistor element shown in FIGS. 6A and 6B is disclosed.
This chip-type thermistor element 51 has a thermistor body 52 having a rectangular shape. In the thermistor body 52, a plurality of first inner electrodes 53a to 53g, and a plurality of second inner electrodes 54a to 54g are provided. The first inner electrodes 53a to 53g extend out to a first end surface 52a, while the second inner electrodes 54a to 54g extend out to a second end surface 52b. First and second outer electrodes 55 and 56 are disposed on the first and second end surfaces, respectively.
In this chip-type thermistor element 51, as shown by the inner electrodes 53a and 54a as an example, the tip of one first inner electrode and that of one second inner electrode are arranged with a gap xe2x80x9caxe2x80x9d interposed therebetween. In the case of the chip-type thermistor element 51, the gaps xe2x80x9caxe2x80x9d are formed at positions that are alternately different in the lamination direction. For example, the gap xe2x80x9caxe2x80x9d between the first inner electrode 53aand the second inner electrode 54a defining the uppermost layer is located near the end surface 52a, while the gap formed at the next vertical level in the lamination direction, i.e., the gap between the inner electrode 53b and the inner electrode 54b, is formed near the end surface 52b. 
In this manner, an attempt at reducing the resistance is made by arranging a plurality of gap positions at different locations along the lamination direction.
In addition, as shown in FIG. 6B, as compared with the inner electrodes 53a and 54a located at the uppermost portion, the inner electrodes 53b and 54b located at the next vertical position have a small dimension in the widthwise direction, thereby reducing the variations in the resistance value caused by a laminate shear that occurs between inner electrodes.
Thus, in the chip-type thermistor element 51, the positions of gaps between the first and second inner electrodes are mutually different in the longitudinal direction. More specifically, the gap xe2x80x9caxe2x80x9d is located near one outer electrode 55, or near the other outer electrode 56.
As a result, the distance Z between the inner electrode 54a situated in the uppermost layer and the outer electrode 55 having the potential opposite to the potential of the outer electrode 56, to which the inner electrode 54ais connected, becomes small.
Typically, the above-described inner electrodes 53a to 54g are formed by screen-printing a conductive paste on a ceramic green sheet. The outer electrodes 55 and 56 are formed by applying a conductive paste via a dipping method, and by printing the paste. Therefore, variations of the electrode covering portions of the outer electrodes 55 and 56 in the length E are usually larger than those of the gap xe2x80x9caxe2x80x9d in the longitudinal dimension.
Hence, if the distance Z in FIG. 6 approaches the longitudinal dimension of the gap xe2x80x9caxe2x80x9d, or becomes smaller than the longitudinal dimension of the gap xe2x80x9caxe2x80x9d, the contribution to the total resistance value from between the outer electrode 55 and the inner electrode 54a will become larger than that between the inner electrodes 53a and 54a. This raises a problem in that, as the distance Z decreases, variations of the chip-type thermistor element 51 in the resistance value increases because of variations of the covering portion of the outer electrode 55 in the longitudinal dimension E.
In order to overcome the problems described above, preferred embodiments of the present invention provide a chip-type resistor element which minimizes and eliminates variations in the resistance value caused by forming accuracy of the outer electrodes, and which has thereby very low variations in the resistance value, by improving the chip-type resistor element which is, as described above, capable of reducing the resistance value, and minimizing the variations in the resistance value caused by inter-laminate shear.
In accordance with a first preferred embodiment of the present invention, a chip-type resistor element includes a resistor body having first and second end surfaces which are opposite to each other, a plurality of first inner electrodes disposed in the resistor and extending out to the first end surface, a plurality of second inner electrodes disposed in the resistor and extending out to the second end surface, and the tip of each of which is opposed to the tip of a corresponding first inner electrode with a gap interposed therebetween, and first and second outer electrodes which cover the first and second end surfaces, respectively, and each of which has an electrode covering portion reaching the top surface, bottom surface, and a pair of side surfaces of the resistor body. In this chip-type resistor element, the positions of the gaps between the first inner electrodes and the corresponding second inner electrodes are different in the longitudinal direction, where the longitudinal direction is the direction connecting the first and second end surfaces. This chip-type resistor element also includes third inner electrodes which are disposed closer to the outside of the resistor body in the lamination direction than the first and second inner electrodes on the outermost sides in the lamination direction, which are connected to the outer electrode near the gaps between the first and second inner electrodes on the outermost sides, and which are arranged to extend to closer to the inside in the longitudinal direction than the gaps between the first and second inner electrodes on the outermost sides.
In the first preferred embodiment of the present invention, it is preferable that the chip-type resistor element in accordance with the present invention also include fourth inner electrodes, the tip of each of which is opposed to a corresponding third electrode with a gap interposed therebetween, and which are electrically connected to the outer electrode opposite to the outer electrode to which the third inner electrodes are connected.
In accordance with a second preferred embodiment of the present invention, a chip-type resistor element includes a resistor body having first and second end surfaces that are opposite with each other, a plurality of first inner electrodes disposed in the resistor and extending out to the first end surface, a plurality of second inner electrodes disposed in the resistor and extending out to the second end surface, and the tip of each of which is opposed to the tip of a corresponding first inner electrode with a gap interposed therebetween, first and second outer electrodes arranged to cover the first and second end surfaces, respectively, and each of which has an electrode covering portion extending to the top and bottom surfaces of the resistor body and a pair of side surfaces thereof. In this chip-type resistor element, the positions of the gaps between the first inner electrodes and the corresponding second inner electrodes are different in the longitudinal direction, where the longitudinal direction is the direction connecting the first and second end surfaces. Also, the gap between the first and second inner electrodes on the outermost side in the lamination direction, is located closer to the inside of the resistor body in the longitudinal direction than the inside ends of the electrode covering portions of the first and second outer electrodes.
In the chip-type resistor element in accordance with various preferred embodiments of the present invention, it is preferable that each of the first inner electrodes and a corresponding second inner electrode which is opposed to the first inner electrode with a gap interposed therebetween, be positioned on the same plane.
In the chip-type resistor element in accordance with various preferred embodiments of the present invention, it is further preferable that the resistor body be a thermistor body, and that a thermistor element be constituted of the thermistor body.
The above and other elements, characteristics, features, and advantages of the present invention will be clear from the following detailed description of preferred embodiments of the invention in conjunction with the accompanying drawing. In the drawing, like elements in each of the several figures are identified by the same reference numeral.